'All 0 credential(s) exhausted for <provider>' did not match _is_quota_error_text
so it fell through to a generic 'Error' with no hint (the exception path's else
branch discarded the hint entirely). Adds a distinct credential_pool_empty
classification (ordered before the quota check) + an explicit exception-path
branch + an actionable pool-specific hint, so the user sees why the turn failed
and what to do. Does not over-match (doesn't swallow real quota errors) and
doesn't block partial-harvest; downstream tolerates the new type.
NOTE: this is the CLASSIFICATION half of #3929 only — the data-loss half
(reasoning/partial-work restore on reload-reconcile) is a scoped follow-up that
needs the reporter's server logs.
Self-built (nesquena-hermes); nesquena independent review APPROVED.